Solid-state image sensor with micro-lenses for anti-shading

Abstract

A solid-state image sensor prevents shading while maintaining the wider dynamic range of an image signal without reducing its optical resolution. The image sensor has plural pairs of higher- and lower-sensitivity photodiodes and micro-lenses each of which is provided over particular one of the higher- and lower-sensitivity photodiodes for collecting the light incident on corresponding one of the higher- and lower-sensitivity photodiodes. The micro-lenses provided over the lower-sensitivity photodiodes have the curvature thereof smaller than that of the other micro-lenses, thereby providing for the lower-sensitivity photodiode a significant amount of light even for a change of the exit pupil position or incident angle or the like that causes the position of an image circle to shift.

1. A solid-state image sensor comprising:
 a plurality of first photodiodes and a plurality of second photodiodes of sensitivity lower than said first photodiodes which are disposed in a virtual plane for receiving light incident from a field of view to be captured; 
 a plurality of first micro-lenses each being provided over particular one of said first photodiodes for collecting the light incident on said particular first photodiode; 
 a plurality of second micro-lenses each being provided over particular one of said second photodiodes for collecting the light incident on said particular second photodiode, at least one of said second micro-lenses having a curvature smaller than that of said first micro-lenses; and 
 an optical shielding film having first openings located above said first photodiodes and second openings located above said second photodiodes associated with said second micro-lenses, one of said second openings being smaller than one of said first openings and said smaller curvature second micro-lens being located over said smaller second opening; 
 a plurality of first in-layer lenses each being provided between one of said first openings and corresponding one of said first micro-lenses for further collecting the light collected by said first micro-lens on said first photodiode; and 
 a plurality of second in-layer lenses each being provided between corresponding one of said second openings and corresponding one of said second micro-lenses for further collecting the light collected by said second micro-lens on said second photodiode, at least one of said second in-layer lenses having a curvature smaller than the curvature of one of said first in-layer lenses, 
 wherein said curvature of said second micro-lens is smaller by an amount determined based on a size of said second opening. 
 
     
     
       2. The solid-state image sensor in accordance with  claim 1 , wherein at least one of said second micro-lenses has substantially zero curvature. 
     
     
       3. The solid-state image sensor in accordance with  claim 1 , further comprising a covering element provided over said first and second micro-lenses for preventing a foreign material from being caught in a space between adjacent ones of said first and second micro-lenses. 
     
     
       4. The solid-state image sensor in accordance with  claim 3 , wherein said covering element has a refractive index lower than said first and second micro-lenses, and is optically substantially transparent and planar. 
     
     
       5. The solid-state image sensor in accordance with  claim 3 , wherein said covering element is a film for planarizing the convex or concave of said first and second micro-lenses. 
     
     
       6. The solid-state image sensor in accordance with  claim 1 , wherein said at least one second in-layer lens has substantially zero curvature. 
     
     
       7. The solid-state image sensor in accordance with  claim 1 , wherein said optical shielding film provides different sized optical openings for said first photodiodes as compared to said second photodiodes. 
     
     
       8. The solid-state image sensor in accordance with  claim 1 , wherein said at least one of said second micro-lenses has said curvature smaller than the curvature of said one of said first micro-lenses, thereby providing a larger image circle for said second photodiode. 
     
     
       9. The solid-state image sensor in accordance with  claim 1 , wherein an amount by which said curvature is smaller is determined based on a sensitivity difference between said first and said second photodiodes. 
     
     
       10. The solid-state image sensor in accordance with  claim 1 , wherein an amount by which said curvature is smaller is determined such that said image sensor maintains a sensitivity ratio between said first and said second photodiodes. 
     
     
       11. The solid-state image sensor in accordance with  claim 1 , wherein an amount by which said curvature is smaller is determined such that said image sensor maintains a sensitivity ratio between said first and said second photodiodes equal to 16 to 1. 
     
     
       12. The solid-state image sensor in accordance with  claim 1 , wherein an amount by which said curvature is smaller is determined such that an image circle formed by collected incident light for said second photodiode has its periphery outside said opening. 
     
     
       13. A solid-state image sensor comprising:
 a plurality of first photodiodes and a plurality of second photodiodes of sensitivity lower than said first photodiodes which are disposed in a virtual plane for receiving light incident from a field of view to be captured; 
 a plurality of first micro-lenses each being provided over particular one of said first photodiodes for collecting the light incident on said particular first photodiode; 
 a plurality of second micro-lenses each being provided over particular one of said second photodiodes for collecting the light incident on said particular second photodiode; 
 an optical shielding film having first openings located above said first photodiodes and second openings located above said second photodiodes associated with said second micro-lenses, one of said second openings being smaller than one of said first openings; 
 a plurality of first in-layer lenses each being provided between corresponding one of said first openings and corresponding one of said first micro-lenses for further collecting the light collected by said first micro-lens on said first photodiode; and 
 a plurality of second in-layer lenses each being provided between corresponding one of said second openings and corresponding one of said second micro-lenses for further collecting the light collected by said second micro-lens on said second photodiode, 
 wherein at least one of said second micro-lenses and said second in-layer lenses have a curvature smaller than that of said first micro-lenses, and said smaller curvature second micro-lens is located over said smaller second opening, to allow one of said second photodiodes to be provided with a larger image area so that said image sensor is less affected by a change of an exit pupil position or an incident angle of a light beam, wherein an amount by which said curvature is smaller is determined such that an image circle formed by collected incident light for said second photodiode has its periphery outside said optical shielding film opening located above said second photodiode. 
 
     
     
       14. The solid-state image sensor in accordance with  claim 13 , wherein said curvature of said at least one of said second micro-lenses has a value that allows said one of said second photodiodes to be exposed to at least a certain amount of light even for a change of said exit pupil position or incident angle that shifts the position of an image area formed by collected incident light for said one of said second photodiodes. 
     
     
       15. The solid-state image sensor in accordance with  claim 13 , wherein said curvature of said at least one of said second micro-lenses is modified so as to widen said image area provided for said one of said second photodiodes, and the sensitivity ratio between said first and said second photodiodes is adjusted by adjusting sizes of respective openings created above said photodiodes in optical shielding films, or by differentiating an exposure time or an optical transmittance associated with respective photodiodes. 
     
     
       16. A solid-state image sensor comprising:
 a first photodiode and a second photodiode of sensitivity lower than said first photodiode which are disposed in a virtual plane for receiving light incident from a field of view to be captured, wherein said first and second photodiodes work together as one pixel; 
 a first micro-lens provided over said first photodiode for collecting the light incident on said first photodiode; and 
 a second micro-lens provided over said second photodiode for collecting the light incident on said second photodiode, said second micro-lens having a curvature smaller than that of said first micro-lens, 
 an optical shielding film having a first opening located above said first photodiode and a second opening located above said second photodiode associated with said second micro-lens, said second opening being smaller than said first opening and said smaller curvature second micro-lens being located over said smaller second opening; 
 a first in-layer lens provided between said first opening and said first micro-lens for further collecting the light collected by said first micro-lens on said first photodiode; and 
 a second in-layer lens provided between said second opening and said second micro-lens for further collecting the light collected by said second micro-lens on said second photodiode, said second in-layer lens having a curvature smaller than that of said first in-layer lens, 
 wherein said second micro-lens curvature is smaller than said first micro-lens curvature by an amount determined based on sensitivities of said first and second photodiodes within said one pixel, said smaller curvature being such that an image circle formed by collected incident light for said second photodiode has its periphery outside said optical shielding film opening located above said second photodiode. 
 
     
     
       17. The solid-state image sensor in accordance with  claim 16 , wherein an amount by which said curvature is smaller is determined based on a sensitivity difference between said first and said second photodiodes. 
     
     
       18. The solid-state image sensor in accordance with  claim 16 , wherein an amount by which said curvature is smaller is determined such that said image sensor maintains a sensitivity ratio between said first and said second photodiodes.